Abyssal Clay Research Articles

Exploring the abundance, metabolic potential and gene expression of subseafloor Chloroflexi in million-year-old oxic and anoxic abyssal clay.

ABSTRACTChloroflexi are widespread in subsurface environments, and recent studies indicate that they represent a major fraction of the communities in subseafloor sediment. Here, we compare the abundance, diversity, metabolic potential and gene expression of Chloroflexi from three abyssal sediment cores from the western North Atlantic Gyre (water depth >5400 m) covering up to 15 million years of sediment deposition, where Chloroflexi were found to represent major components of the community at all sites. Chloroflexi communities die off in oxic red clay over 10–15 million years, and gene expression was below detection. In contrast, Chloroflexi abundance and gene expression at the anoxic abyssal clay site increase below the seafloor and peak in 2–3 million-year-old sediment, indicating a comparably higher activity. Metatranscriptomes from the anoxic site reveal increased expression of Chloroflexi genes involved in cell wall biogenesis, protein turnover, inorganic ion transport, defense mechanisms and prophages. Phylogenetic analysis shows that these Chloroflexi are closely related to homoacetogenic subseafloor clades and actively transcribe genes involved in sugar fermentations, gluconeogenesis and Wood–Ljungdahl pathway in the subseafloor. Concomitant expression of cell division genes indicates that these putative homoacetogenic Chloroflexi are actively growing in these million-year-old anoxic abyssal sediments.

Study on the applicability of the strip probe in detecting the strength of soft clay

ABSTRACT As ocean engineering has developed towards the deep sea, a precise instrument is urgently needed to accurately measure the in situ strength of soft clay at the shallow strata of the deep sea and thus to evaluate the bearing capacity of the foundation. In this paper, a new type of probe – the strip probe – is introduced. The soft clay failure modes, including the shallow penetration and deep penetration of the strip probe, were analysed by a centrifugal model test and the mesh-to-mesh solution mapping (MMSM) finite element method. Based on limit analysis, the upper-bound solutions between the soft clay strength and the strip probe penetration resistance were established under non-full-flow and full-flow modes. Through an in site penetration test, the upper-bound solutions were proven rational, and the strip probe was appropriate for detecting the strength of abyssal soft clay.

Mass wasting and hiatuses during the Cretaceous-Tertiary transition in the North Atlantic: Relationship to the Chicxulub impact?

Deep-sea sections in the North Atlantic are claimed to contain the most complete sedimentary records and ultimate proof that the Chicxulub impact is Cretaceous-Tertiary boundary (KTB) in age and caused the mass extinction. A multi-disciplinary study of North Atlantic DSDP Sites 384, 386 and 398, based on high-resolution planktonic foraminiferal biostratigraphy, carbon and oxygen stable isotopes, clay and whole-rock mineralogy and granulometry reveals the age, stratigraphic completeness and nature of sedimentary disturbances. Results show a major hiatus across the KTB at Site 384 with Zones CF1, P0 and P1a missing, spanning at least ~540ky, similar to other North Atlantic and Caribbean localities associated with tectonic activity and Gulf Stream erosion. At Sites 386 and 398, discrete intervals of disturbed sediments with mm-to-cm-thick spherule layers have previously been interpreted as the result of impact-generated earthquakes at the KTB destabilizing continental margins prior to settling of impact spherules. However, improved age control based on planktonic foraminifera indicates spherule deposition in the early Danian Zone P1a(2) (upper Parvularugoglobigerina eugubina Zone) more than 100ky after the KTB. At Site 386, two intervals of white chalk contain very small (<63μm) early Danian Zone P1a(2) assemblages (65%) and common reworked Cretaceous (35%) species. In contrast, the in situ red-brown and green abyssal clays of this core are devoid of carbonate. In addition, high calcite, mica and kaolinite and upward-fining are observed in the chalks, indicating downslope transport from shallow waters and sediment winnowing via distal turbidites. At Site 398, convoluted red to tan sediments with early Danian and reworked Cretaceous species represent slumping of shallow water sediments as suggested by dominance of mica and low smectite compared to in situ deposition. We conclude that mass wasting was likely the result of earthquakes associated with increased tectonic activity in the Caribbean and the Iberian Peninsula during the early Danian well after the Chicxulub impact.

Epithermal neutron activation analysis investigation of Clarion-Clipperton abyssal plane clay and polymetallic micronodules

The content of seven major (Na, Al, Cl, Mn, K, Ca, Ti, Fe) and 30 trace (Sc, V, Cr, Ni, Co, Zn, Cu, As, Sr, Rb, Zr, Mo, Sn, In, Sb, Ba, Cs, La, Ce, Nd, Eu, Sm, Tb, Dy, Yb, Hf, Ta, W, Th, U) elements determined by INAA in 13 samples of abyssal clay and two samples of micronodules collected from the North pacific Ocean Clarion-Clipperton abyssal plane is presented and discussed with respect to some rocks models.

Major and trace element distributions in manganese nodules and micronodules as well as abyssal clay from the Clarion-Clipperton abyssal plain, Northeast Pacific

The contents of seven major components (TiO2, Fe2O3, MgO, CaO, Na2O, K2O and P2O5) and 15 trace elements (Sc, V, Cr, Ni, Cu, Sr, Y, Zr, Ba, La, Ce, Nd, Eu, Yb and Th) were determined by ICP-AE spectrometry in 27 samples of manganese nodules, micronodules as well as abyssal clay collected by dredging from an area of nearly 1,9802 nautical miles in the central Clarion-Clipperton abyssal plain at a depth of about 4,500 m. Statistical analyses were used to compare among individual as well as pooled datasets, in addition to different indicators such as La/Th, Ni/Cu and LREE/HREE ratios for the Clarion-Clipperton samples, as well as between these and corresponding values for the upper continental crust (UCC), North America Shale Composite (NASC), and igneous Indian and Pacific Mid-Ocean Ridge Basalts (MORBs). The results show significant correlations between major components in the Clarion-Clipperton samples and Pacific Ocean MORB, whereas trace elements (excepting Ni and Cu) correlate better with the UCC and NASC. There is also depletion in LREEs, together with a Ce negative anomaly for all Clarion-Clipperton samples. The nodule, micronodule and abyssal clay datasets each reveal typical clusters of components such as P2O5 and Y, La, Nd, Eu, Tb, or Ni and Cu. Compared to abyssal clay, the nodule as well as micronodules show significant enrichment in Ni and Cu; nevertheless, an essentially constant Ni/Cu ratio indicates that all samples come from the sediment surface. The distributions of major components as well as trace elements for the Clarion-Clipperton samples present, to different degrees, characteristics common to both the upper continental crust and Mid-Ocean Ridge Basalt, strongly implying a hydrothermal origin, most probably from East Pacific Rise material transported by the Pacific North Equatorial Current.

Geochemical studies with abyssal Red clays

Abstract Pertinent geochemical phenomena required to assess the feasibility of emplacing high‐level radioactive waste in subseabed formations are being identified and experimentally investigated. The geologic formation selected for study is the abyssal red clay. Investigations of phenomena occurring in the sediment beyond the hydrothermal environment associated with the waste have focused on sorption equilibria, solution chemistry of the actinides, and radionuclide diffusion experiments. Most data from the diffusion experiments are consistent with the experimentally observed sorption equilibria. Studies of processes occurring in the hydrothermal environment near the canister have addressed heat‐induced sediment‐seawater interactions and their effects on canister, waste form, and radionuclide source term. Significant changes in oxidation potential and pH have been found in the hydrothermal environment and are related to variations in temperature and mineralogy. Studies of processes occurring near the sedim...

A summary of Deep Sea Drilling Project Leg 67 shipboard results from the Mid-America Trench transect off Guatemala

Summary The Middle America Trench off Guatemala was transected by 24-channel seismic reflection surveys, seismic-refraction surveys, and drilling with the Glomar Challenger . The drilling was done at three sites on the oceanic Cocos plate and four sites on the Caribbean plate. These plates converge at about 10 cm yr −1 . At all drill sites sediment of upper Miocene to Quaternary age is almost entirely hemipelagic mud with interbedded thin volcanic ash, except in the trench where mud and fine sand turbidites less than 400 000 yr old are ponded. However, the underlying rocks are very different. On the oceanic Cocos plate a basal chalk sequence of lower and middle Miocene age is overlain by a thin section of abyssal clay. At a site only 3 km landward of the trench axis where drilling penetrated the slope deposits we recovered a Cretaceous to lower Miocene claystone sequence resting on a section containing igneous rock of continental affinity. A large net subduction of sediment along with ocean crust has occurred during the present (Miocene-Quaternary) episode of subduction and perhaps parts of the continental framework have been subducted as well. However, no current model satisfactorily explains the surprising occurrence of Cretaceous-Miocene claystone at the foot of the trench slope.

Subseabed Disposal of Nuclear Wastes

Fine-grained clay formations within stable (predictable) deep-sea regions away from lithospheric plate boundaries and productive surface waters have properties that might serve to permanently isolate radioactive waste. The most important characteristics of such clays are their vertical and lateral unifomity, low permeability, very high cation retention capacity, and potential for self-healing when disturbed. The most attractive abyssal clay formation (oxidized red ciay)covers nearly 30 percent of the sea floor and hence 20 percent of the earth's surface.

Sedimentologic Aspects of Bioturbation in Abyssal Atlantic Ocean: ABSTRACT

Relations between bioturbation features and sedimentologic aspects of abyssal pelagic ooze and clay were investigated in 26 box cores collected in 1,400 to 5,700 m of water in the central and southern Atlantic Ocean. Sediment composition, texture, and core stratigraphy were compared with the occurrences of biogenic structures and other aspects of bioturbation to determine the sedimentologic factors that most affect burrow preservation and biologic mixing of abyssal sediment. Box core surfaces typically exhibited a heterogeneous microtopography of mounds, lumps, trails, agglutinated tubes, and open holes. Benthic protists (foraminifera and xenophyophorids) and fecal strings of larger organisms were common. Remnants of shallow infaunal tunnel systems sometimes were evident on slightly washed box core surfaces. For example, Paleodictyon occurred in carbonate-rich ooze; Cosmorhaphe occurred in deposits containing 20 to 30% coarse fraction; and Spirorhaphe appeared to be cosmopolitan with respect to sediment type. Sediments of the mixed layer (upper 5 to 8 cm) and underlying Holocene transition layer were compared with respect to carbonate, organic carbon, and coarse fraction (> 62µm) percentages. Transition layer sediments, which contained the most visible burrows, were much more heterogeneous in terms of carbonate content than mixed layer deposits. However, the heterogeneity of organic carbon and coarse fraction concentrations were roughly equivalent in the two horizons. Visibility of specific burrows was highest in cores with low carbonate contents ( 70% CaCO3) throughout the entire core. End_of_Article - Last_Page 962------------

Meteoroid ablation spheres from deep-sea sediments

We present analyses of spheres magnetically extracted from mid-Pacific abyssal clays 0–500,000 years old. The concentration of spheres >200 μm is a few times 10 ppb. The spheres were divided into three groups using their dominant mineralogy, and are named iron, glassy, and silicate. Most spheres were formed from particles that completely melted as they separated from their parent meteoroids during the ablation process. However, some of the silicate spheres contain relict grains of the parent meteoroids that did not experience any melting. Typically, these relict grains are olivine crystals whose cores are Mg-rich (Fo 89–99). Commonly the outer rims of these grains were altered during heating. Other relict mineral grains include enstatite, ferrous spinel, chromite, and pentlandite. The three groups of spheres may possibly indicate some genetic significance. It seems reasonable to expect iron-rich spheres to be produced during ablation of iron and metal-rich silicate meteoroids. Metal spheres are probably not produced by ablation of predominantly silicate meteoroids because studies of fusion crusts and laboratory ablated silicate materials have never yielded separate metal spheres, but rather have produced spheres with intergrown iron oxide and silicate phases. The iron spheres possess identical mineralogy with the fusion crusts of Boguslavka, Norfork, and N'Kandhla iron meteorites as well as with the ablation debris created in the laboratory using iron and nickel-iron samples. The glassy spheres are considerably more Fe-rich than the silicate spheres. They consist of magnetite and a Fe-rich glass which is relatively low in Si. Some of these spheres may have experienced pronounced volatile depletion during the ablation process and could have been derived from silicate or metal-rich silicate meteoroids. The silicate spheres are undoubtedly derived from ablation of stony meteoroids. Two of the mineral assemblages occurring in these spheres (olivine-magnetite-glass and sulfide) are identical to those described in the natural fusion crusts of Allende, Orgueil, and Murchison meteorites, laboratory-made ablation debris, and melted interplanetary dust collected from the stratosphere. Bulk compositions and relict grains are useful for determining the parent meteoroid types for the silicate spheres. Bulk analyses of spheres have non-volatile elemental abundances similar to chondritic abundances. Analyses of relict grains identified high-temperature minerals which often occur as larger crystals in a fine-grained matrix that is characterized by voids. These voids were caused by escaping volatiles as minerals decomposed during ablation. Because larger crystals of higher-temperature minerals are associated with fine-grained, low-temperature, volatile-rich matrix, the obvious candidates for parent meteoroids of the silicate spheres containing relict grains are carbonaceous chondrites.

Organic 14C activity in an abyssal marine sediment

ONE measure of transport rates and residence times of organic carbon within the various organic carbon pools in the ocean is to follow perturbations from the 1952–58 and 1961–62 atmospheric thermonuclear bomb tests on the natural 14C activities of living, detrital and dissolved organic matter. We report here our measurement of the 14C activity of the total sedimentary organic carbon (SOC) in an abyssal red clay, as no such data were available for this organic carbon pool. Ultimately, these sedimentary organic 14C activities may be compared with the 14C activity of the source organic material in the water column and estimates made of the magnitude of organic carbon consumption at the seawater–sediment interface. What was found, unexpectedly, was evidence for the penetration of recent organic carbon from the 4 cm mixed layer at the sediment–seawater interface down to at least 12 cm in the sedimentary column. This suggests a different and more rapid mechanism for the sedimentation of some fraction of the SOC other than direct association with clay minerals.

Geological History of the Western North Pacific

A considerable portion of the abyssal floor of the western North Pacific was already receiving pelagic sediment in late Jurassic time. Carbonate sediments were later replaced by abyssal clays as the basin deepened and bottom waters became more aggressive. The resulting facies boundary, which can be recognized on seismic profiles, is broadly transgressive; it ranges in age from mid-Cretaceous in the western Pacific to Oligocene in the central Pacific. Cherts are encountered at and below the major facies boundary and appear to have been formed by postdepositional processes.

Sedimentation in the Puerto Rico Trench

ABSTRACT Holocene, Pleistocene, Tertiary and Upper Cretaceous sediments occur in the Puerto Rico Trench area. The Holocene sediments include mainly brown pteropod and foraminiferal oozes on the slope and brown abyssal clays in the hilly parts of the lower Trench and on the Outer. Ridge. The south wall scarp consists mostly of gray-green Miocene days and scree slopes containing serpentine and limestone rubble. Soft sediments overlie Upper Cretaceous andesitic volcanics, radiolarian cherts and foraminiferal cherty marls on the faulted North Wall. Color, texture, and composition of beds in ten cores 3 to 10 m long from the floor of the Puerto Rico Trench form the basis for correlation of graded beds several millimeters to 7 m thick over distances of 200 km. There is a general decrease in grain si e of the coarsest detritus and the thickness of the basal sandy section in each graded bed down a high level abyssal plain, into and along the abyssal plain of the lower Trench floor. Thick beds of megascopically homogeneous silty clay, commonly burrowed in their uppermost 10 to 20 cm, make up most of the graded beds in the deepest part of the lower Trench floor. Variation in bottom topography and sediment properties show that the layers were deposited by turbidity currents originating near the Puerto Rico-Virgin Islands shelf and flowing through numerous canyons northwestward down a high-level abyssal plain and into the lower main trench plain on which they spread laterally. In at least two instances the turbidity currents were powerful enough to deposit 20 to 50 cm of fine sand 100 km way from and 10 m above the point which they entered the main trench floor.